Periodontal inflammation and bone loss in aged mice

Associations between immune-inflammatory markers, age, and periodontal status: a cross-sectional study

Since periodontal disease is associated with many systemic diseases, it is important to evaluate its effects on host responses in elderly individuals. To this end, this study investigated salivary interleukin (IL)-17, IL-18, toll-like receptor (TLR) 2, TLR4, and tumor necrosis factor-alpha (TNF-α) levels in patient groups with different periodontal health statuses and immunologically evaluated the relationship between age and periodontal health status. A total of 60 individuals aged 18-40 years (young individuals) and 60 individuals aged 65 years or older (elderly individuals) were included in this study. According to periodontal disease status, the patients were divided into periodontally healthy, gingivitis, and periodontitis subgroups. Clinical periodontal parameters, including probing depth (PD), clinical attachment level (CAL), plaque index (PI), and gingival index (GI), were recorded. Saliva samples were collected and analyzed using ELISA to determine the levels of IL-17, IL-18, TLR2, TLR4, and TNF-α. Higher clinical periodontal parameter (PD, CAL, PI, and GI) and inflammatory marker (IL-17, IL-18, TNF-α, TLR2, and TLR4) levels were found in patients with periodontitis than those in periodontally healthy individuals and patients with gingivitis (P < 0.05). Salivary inflammatory marker levels were significantly higher in elderly individuals than those in young individuals in all subgroups (P < 0.05). A positive correlation was found between inflammatory marker levels and clinical periodontal parameters, but there was no correlation between TLR2 and PI or GI. This study suggests a significant increase in host response to periodontal disease as the disease progresses, with the levels of cytokines and TLR expression exhibiting an increasing trend with age. Increased IL-17, IL-18, TLR2, TLR4, and TNF-α levels in elderly individuals in all periodontal health subgroups might suggest the role of these cytokines and TLR pathway in the pathogenesis of periodontal diseases.

Periodontal disease as a model to study chronic inflammation in aging

Periodontal disease is a chronic inflammatory condition that results in the destruction of the teeth supporting tissues, eventually leading to the loss of teeth and reduced quality of life. In severe cases, periodontal disease can limit proper nutritional intake, cause acute pain and infection, and cause a withdrawal from social situations due to esthetic and phonetic concerns. Similar to other chronic inflammatory conditions, periodontal disease increases in prevalence with age. Research into what drives periodontal disease pathogenesis in older adults is contributing to our general understanding of age-related chronic inflammation. This review will present periodontal disease as an age-related chronic inflammatory disease and as an effective geroscience model to study mechanisms of age-related inflammatory dysregulation. The current understanding of the cellular and molecular mechanisms that drive inflammatory dysregulation as a function of age will be discussed with a focus on the major pathogenic immune cells in periodontal disease, which include neutrophils, macrophages, and T cells. Research in the aging biology field has shown that the age-related changes in these immune cells result in the cells becoming less effective in the clearance of microbial pathogens, expansion of pathogenic subpopulations, or an increase in pro-inflammatory cytokine secretions. Such changes can be pathogenic and contribute to inflammatory dysregulation that is associated with a myriad of age-related disease including periodontal disease. An improved understanding is needed to develop better interventions that target the molecules or pathways that are perturbed with age in order to improve treatment of chronic inflammatory conditions, including periodontal disease, in older adult populations.

Changes in oral health during aging in a novel non-human primate model

Oral health plays a significant role in the quality of life and overall well-being of the aging population. However, age-related changes in oral health are not well understood due to challenges with current animal models. In this study, we analyzed the oral health and microbiota of a short-lived non-human primate (i.e., marmoset), as a step towards establishing a surrogate for studying the changes that occur in oral health during human aging. We investigated the oral health of marmosets using cadaveric tissues in three different cohorts: young (aged ≤6 years), middle-aged, and older (>10 years) and assessed the gingival bacterial community using analyses of the V3-V4 variable region of 16S rRNA gene. The oldest cohort had a significantly higher number of dental caries, increased dental attrition/erosion, and deeper periodontal pocket depth scores. Oral microbiome analyses showed that older marmosets had a significantly greater abundance of Escherichia-Shigella and Propionibacterium, and a lower abundance of Agrobacterium/Rhizobium at the genus level. Alpha diversity of the microbiome between the three groups showed no significant differences; however, principal coordinate analysis and non-metric multidimensional scaling analysis revealed that samples from middle-aged and older marmosets were more closely clustered than the youngest cohort. In addition, linear discriminant analysis effect size (LEFSe) identified a higher abundance of Esherichia-Shigella as a potential pathogenic biomarker in older animals. Our findings confirm that changes in the oral microbiome are associated with a decline in oral health in aging marmosets. The current study suggests that the marmoset model recapitulates some of the changes in oral health associated with human aging and may provide opportunities for developing new preventive strategies or interventions which target these disease conditions.

A novel macrolide-Del-1 axis to regenerate bone in old age

Aging is associated with increased susceptibility to chronic inflammatory bone loss disorders, such as periodontitis, in large part due to the impaired regenerative potential of aging tissues. DEL-1 exerts osteogenic activity and promotes bone regeneration. However, DEL-1 expression declines with age. Here we show that systemically administered macrolide antibiotics and a non-antibiotic erythromycin derivative, EM-523, restore DEL-1 expression in 18-month-old ("aged") mice while promoting regeneration of bone lost due to naturally occurring age-related periodontitis. These compounds failed to induce bone regeneration in age-matched DEL-1-deficient mice. Consequently, these drugs promoted DEL-1-dependent functions, including alkaline phosphatase activity and osteogenic gene expression in the periodontal tissue while inhibiting osteoclastogenesis, leading to net bone growth. Macrolide-treated aged mice exhibited increased skeletal bone mass, suggesting that this treatment may be pertinent to systemic bone loss disorders. In conclusion, we identified a macrolide-DEL-1 axis that can regenerate bone lost due to aging-related disease.

The rosetta stone of successful ageing: does oral health have a role?

Ageing is an inevitable aspect of life and thus successful ageing is an important focus of recent scientific efforts. The biological process of ageing is mediated through the interaction of genes with environmental factors, increasing the body's susceptibility to insults. Elucidating this process will increase our ability to prevent and treat age-related disease and consequently extend life expectancy. Notably, centenarians offer a unique perspective on the phenomenon of ageing. Current research highlights several age-associated alterations on the genetic, epigenetic and proteomic level. Consequently, nutrient sensing and mitochondrial function are altered, resulting in inflammation and exhaustion of regenerative ability.Oral health, an important contributor to overall health, remains underexplored in the context of extreme longevity. Good masticatory function ensures sufficient nutrient uptake, reducing morbidity and mortality in old age. The relationship between periodontal disease and systemic inflammatory pathologies is well established. Diabetes, rheumatoid arthritis and cardiovascular disease are among the most significant disease burdens influenced by inflammatory oral health conditions. Evidence suggests that the interaction is bi-directional, impacting progression, severity and mortality. Current models of ageing and longevity neglect an important factor in overall health and well-being, a gap that this review intends to illustrate and inspire avenues for future research.

IL-1β and TNF-α play an important role in modulating the risk of periodontitis and Alzheimer's disease

BACKGROUND

Systemic activation of the immune system can exert detrimental effects on the central nervous system. Periodontitis, a chronic disease of the oral cavity, is a common source of systemic inflammation. Neuroinflammation might be a result of this to accelerate progressive deterioration of neuronal functions during aging or exacerbate pre-existing neurodegenerative diseases, such as Alzheimer's disease. With advancing age, the progressive increase in the body's pro-inflammatory status favors the state of vulnerability to both periodontitis and Alzheimer's disease. In the present study, we sought to delineate the roles of cytokines in the pathogenesis of both diseases.

METHODS

To examine the impacts of periodontitis on the onset and progression of Alzheimer's disease, 6-month-old female 3 × Tg-AD mice and their age-matched non-transgenic mice were employed. Periodontitis was induced using two different experimental models: heat-killed bacterial-induced periodontitis and ligature-induced periodontitis. To delineate the roles of pro-inflammatory cytokines in the pathogenesis of periodontitis and Alzheimer's disease, interleukin 1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) were also injected into the buccal mandibular vestibule of mice.

RESULTS

Here, we show that IL-1β and TNF-α were two of the most important and earliest cytokines upregulated upon periodontal infection. The systemic upregulation of these two cytokines promoted a pro-inflammatory environment in the brain contributing to the development of Alzheimer's disease-like pathology and cognitive dysfunctions. Periodontitis-induced systemic inflammation also enhanced brain inflammatory responses and subsequently exacerbated Alzheimer's disease pathology and cognitive impairment in 3 × Tg-AD mice. The role of inflammation in connecting periodontitis to Alzheimer's disease was further affirmed in the conventional magnetization transfer experiment in which increased glial responses resulting from periodontitis led to decreased magnetization transfer ratios in the brain of 3 × Tg-AD mice.

CONCLUSIONS

Systemic inflammation resulting from periodontitis contributed to the development of Alzheimer's disease tau pathology and subsequently led to cognitive decline in non-transgenic mice. It also potentiated Alzheimer's disease pathological features and exacerbated impairment of cognitive function in 3 × Tg-AD mice. Taken together, this study provides convincing evidence that systemic inflammation serves as a connecting link between periodontitis and Alzheimer's disease.

Impact of the host response and osteoblast lineage cells on periodontal disease

Periodontitis involves the loss of connective tissue attachment and alveolar bone. Single cell RNA-seq experiments have provided new insight into how resident cells and infiltrating immune cells function in response to bacterial challenge in periodontal tissues. Periodontal disease is induced by a combined innate and adaptive immune response to bacterial dysbiosis that is initiated by resident cells including epithelial cells and fibroblasts, which recruit immune cells. Chemokines and cytokines stimulate recruitment of osteoclast precursors and osteoclastogenesis in response to TNF, IL-1β, IL-6, IL-17, RANKL and other factors. Inflammation also suppresses coupled bone formation to limit repair of osteolytic lesions. Bone lining cells, osteocytes and periodontal ligament cells play a key role in both processes. The periodontal ligament contains cells that exhibit similarities to tendon cells, osteoblast-lineage cells and mesenchymal stem cells. Bone lining cells consisting of mesenchymal stem cells, osteoprogenitors and osteoblasts are influenced by osteocytes and stimulate formation of osteoclast precursors through MCSF and RANKL, which directly induce osteoclastogenesis. Following bone resorption, factors are released from resorbed bone matrix and by osteoclasts and osteal macrophages that recruit osteoblast precursors to the resorbed bone surface. Osteoblast differentiation and coupled bone formation are regulated by multiple signaling pathways including Wnt, Notch, FGF, IGF-1, BMP, and Hedgehog pathways. Diabetes, cigarette smoking and aging enhance the pathologic processes to increase bone resorption and inhibit coupled bone formation to accelerate bone loss. Other bone pathologies such as rheumatoid arthritis, post-menopausal osteoporosis and bone unloading/disuse also affect osteoblast lineage cells and participate in formation of osteolytic lesions by promoting bone resorption and inhibiting coupled bone formation. Thus, periodontitis involves the activation of an inflammatory response that involves a large number of cells to stimulate bone resorption and limit osseous repair processes.

Senescence-associated secretory phenotype and its impact on oral immune homeostasis

The senescence-associated secretory phenotype (SASP), which accumulates over the course of normal aging and in age-related diseases, is a crucial driver of chronic inflammation and aging phenotypes. It is also responsible for the pathogenesis of multiple oral diseases. However, the pathogenic mechanism underlying SASP has not yet been fully elucidated. Here, relevant articles on SASP published over the last five years (2017-2022) were retrieved and used for bibliometric analysis, for the first time, to examine SASP composition. More than half of the relevant articles focus on various cytokines (27.5%), growth factors (20.9%), and proteases (20.9%). In addition, lipid metabolites (13.1%) and extracellular vesicles (6.5%) have received increasing attention over the past five years, and have been recognized as novel SASP categories. Based on this, we summarize the evidences demonstrating that SASP plays a pleiotropic role in oral immunity and propose a four-step hypothetical framework for the progression of SASP-related oral pathology-1) oral SASP development, 2) SASP-related oral pathological alterations, 3) pathological changes leading to oral immune homeostasis disruption, and 4) SASP-mediated immune dysregulation escalating oral disease. By targeting specific SASP factors, potential therapies can be developed to treat oral and age-related diseases.

Does Oral Endotoxin Contribute to Systemic Inflammation?

The oral microbiome, with a unique emphasis on Porphyromonas gingivalis has been associated with a constellation of inflammatory diseases such as cardiovascular disease, rheumatoid arthritis, Alzheimer's disease, type II diabetes, and non-alcoholic associated fatty liver disease. Periodontal disease has also been shown to induce "leaky gut" leading to metabolic endotoxemia. Several recent studies investigating the habitants of the blood microbiome have found the majority of species appear to be derived from oral and skin bacterial communities in otherwise healthy individuals. Many of the same pathologies associated with perturbations of oral health, such as cardiovascular disease, show alterations to the composition of the blood microbiome as well as circulating neutrophil phenotypes. Gingival inflammation is associated with activated blood neutrophil phenotypes that can exacerbate a distal inflammatory insult which may explain the connection between oral and systemic inflammatory conditions. While in the oral cavity, neutrophils encounter oral microbes that are adept in manipulating neutrophil activity which can re-enter the vasculature thereafter. Endotoxin from oral microbes can differ significantly depending on bacterial community and state of oral health to alter cellular LPS tolerance mechanisms which may contribute to the primed neutrophil phenotype seen in periodontitis and provide a mechanism by which the oral-microbes can affect systemic health outcomes. This review synthesizes the studies between inflammatory diseases and oral health with emphasis on microbiome and corresponding lipopolysaccharides in immune tolerance and activation.

Expression of matrix metalloproteinase-3 and -10 is up-regulated in the periodontal tissues of aged mice

Objective

The present study was designed to investigate the whole transcriptome of periodontal tissues of both young and aged mice to identify the characteristic up‐regulation of protease genes with aging and to localize their translated protein products in the periodontal tissues.

Background

The metzincin protease superfamily is composed of matrix metalloproteinases (MMPs), a disintegrin and metalloproteinases, and a disintegrin and metalloproteinases with thrombospondin motifs. Up‐regulation of these extracellular matrix‐degrading proteases has been implicated in senescence of tissues and organs, including the skin. However, few studies have investigated the expression profiles of these proteases and potential involvement in aging of periodontal tissues.

Methods

Periodontal tissues with the surrounding mandibular bones were collected from 50‐ and 10‐week‐old mice. Total RNA was extracted from the periodontal tissue and analyzed by cap analysis of gene expression (CAGE) to identify differentially expressed genes encoding the metzincin proteases. Furthermore, quantitative real‐time polymerase chain reaction (qRT‐PCR) was performed to validate the CAGE results, and the phenotypic expression of proteases involved in aging was localized via immunohistochemical analysis.

Results

The CAGE results showed that the expression levels of MMP‐3, ‐10, and ‐12 were up‐regulated at 50 weeks. Subsequent qRT‐PCR analysis showed that the gene expression levels of MMP‐3 and ‐10 were significantly increased with age. MMP‐10 immunoreactivity was localized exclusively in the cementum and alveolar bone adjacent to the periodontal ligament and was stronger and broader in aged mice than young mice. MMP‐3 immunoreactivity was localized in the periodontal ligaments at both 10 and 50 weeks.

Conclusion

In the present study, we demonstrated that the expression of MMP‐3 and ‐10 increased with aging and identified their characteristic localizations in aged periodontal tissues.

Fibrin is a critical regulator of neutrophil effector function at the oral mucosal barrier

Tissue-specific cues are critical for homeostasis at mucosal barriers. Here, we report that the clotting factor fibrin is a critical regulator of neutrophil function at the oral mucosal barrier. We demonstrate that commensal microbiota trigger extravascular fibrin deposition in the oral mucosa. Fibrin engages neutrophils through the αMβ2 integrin receptor and activates effector functions, including the production of reactive oxygen species and neutrophil extracellular trap formation. These immune-protective neutrophil functions become tissue damaging in the context of impaired plasmin-mediated fibrinolysis in mice and humans. Concordantly, genetic polymorphisms in PLG, encoding plasminogen, are associated with common forms of periodontal disease. Thus, fibrin is a critical regulator of neutrophil effector function, and fibrin-neutrophil engagement may be a pathogenic instigator for a prevalent mucosal disease.

Oral Osteomicrobiology: The Role of Oral Microbiota in Alveolar Bone Homeostasis

Osteomicrobiology is a new research field in which the aim is to explore the role of microbiota in bone homeostasis. The alveolar bone is that part of the maxilla and mandible that supports the teeth. It is now evident that naturally occurring alveolar bone loss is considerably stunted in germ-free mice compared with specific-pathogen-free mice. Recently, the roles of oral microbiota in modulating host defense systems and alveolar bone homeostasis have attracted increasing attention. Moreover, the mechanistic understanding of oral microbiota in mediating alveolar bone remodeling processes is undergoing rapid progress due to the advancement in technology. In this review, to provide insight into the role of oral microbiota in alveolar bone homeostasis, we introduced the term “oral osteomicrobiology.” We discussed regulation of alveolar bone development and bone loss by oral microbiota under physiological and pathological conditions. We also focused on the signaling pathways involved in oral osteomicrobiology and discussed the bridging role of osteoimmunity and influencing factors in this process. Finally, the critical techniques for osteomicrobiological investigations were introduced.

Neutrophils Orchestrate the Periodontal Pocket

The subgingival biofilm attached to tooth surfaces triggers and maintains periodontitis. Previously, late-onset periodontitis has been considered a consequence of dysbiosis and a resultant polymicrobial disruption of host homeostasis. However, a multitude of studies did not show "healthy" oral microbiota pattern, but a high diversity depending on culture, diets, regional differences, age, social state etc. These findings relativise the aetiological role of the dysbiosis in periodontitis. Furthermore, many late-onset periodontitis traits cannot be explained by dysbiosis; e.g. age-relatedness, attenuation by anti-ageing therapy, neutrophil hyper-responsiveness, and microbiota shifting by dysregulated immunity, yet point to the crucial role of dysregulated immunity and neutrophils in particular. Furthermore, patients with neutropenia and neutrophil defects inevitably develop early-onset periodontitis. Intra-gingivally injecting lipopolysaccharide (LPS) alone causes an exaggerated neutrophil response sufficient to precipitate experimental periodontitis. Vice versa to the surplus of LPS, the increased neutrophil responsiveness characteristic for late-onset periodontitis can effectuate gingiva damage likewise. The exaggerated neutrophil extracellular trap (NET) response in late-onset periodontitis is blameable for damage of gingival barrier, its penetration by bacteria and pathogen-associated molecular patterns (PAMPs) as well as stimulation of Th17 cells, resulting in further neutrophil activation. This identifies the dysregulated immunity as the main contributor to periodontal disease.

Methylsulfonylmethane Increases the Alveolar Bone Density of Mandibles in Aging Female Mice

Methylsulfonylmethane (MSM) is a naturally occurring anti-inflammatory compound that effectively treats multiple degenerative diseases such as osteoarthritis and acute pancreatitis. Our previous studies have demonstrated the ability of MSM to differentiate stem cells from human exfoliated deciduous (SHED) teeth into osteoblast-like cells. This study examined the systemic effect of MSM in 36-week-old aging C57BL/6 female mice in vivo by injecting MSM for 13 weeks. Serum analyses showed an increase in expression levels of bone formation markers [osteocalcin (OCN) and procollagen type 1 intact N-terminal propeptide (P1NP)] and a reduction in bone resorption markers [tartrate-resistant acid phosphatase (TRAP) and C-terminal telopeptide of type I collag (CTX-I)] in MSM-injected animals. Micro-computed tomographic images demonstrated an increase in trabecular bone density in mandibles. The trabecular bone density tended to be higher in the femur, although the increase was not significantly different between the MSM- and phosphate-buffered saline (PBS)-injected mice. In mandibles, an increase in bone density with a corresponding decrease in the marrow cavity was observed in the MSM-injected mice. Furthermore, immunohistochemical analyses of the mandibles for the osteoblast-specific marker - OCN, and the mesenchymal stem cell-specific marker - CD105 showed a significant increase and decrease in OCN and CD105 positive cells, respectively. Areas of bone loss were observed in the inter-radicular region of mandibles in control mice. However, this loss was considerably decreased due to stimulation of bone formation in response to MSM injection. In conclusion, our study has demonstrated the ability of MSM to induce osteoblast formation and function in vivo, resulting in increased bone formation in the mandible. Hence, the application of MSM and stem cells of interest may be the right combination in alveolar bone regeneration under periodontal or other related diseases that demonstrate bone loss.

Frailty, aging, and periodontal disease: Basic biologic considerations

Aging is associated with the development of disease. Periodontal disease is one of the many diseases and conditions that increase in prevalence with age. In addition to the traditional focus on individual age-related conditions, there is now a greater recognition that multisystem conditions such as frailty play an important role in the health of older populations. Frailty is a clinical condition in older adults that increases the risk of adverse health outcomes. Both frailty and periodontal disease are common chronic conditions in older populations and share several risk factors. There is likely a bidirectional relationship between periodontal disease and frailty. Comorbid systemic diseases, poor physical functioning, and limited ability to self-care in frail older people have been implicated as underlying the association between frailty and periodontal disease. In addition, both frailty and periodontal disease also have strong associations with inflammatory dysregulation and other age-related pathophysiologic changes that may similarly underlie their development and progression. Investigating age-related changes in immune cells that regulate inflammation may lead to a better understanding of age-related disease and could lead to therapeutic targets for the improved management of frailty and periodontal disease.

Aging-Affected MSC Functions and Severity of Periodontal Tissue Destruction in a Ligature-Induced Mouse Periodontitis Model

Mesenchymal stem cells (MSCs) are known to play important roles in the repair of lost or damaged tissues and immunotolerance. On the other hand, aging is known to impair MSC function. However, little is currently known about how aged MSCs affect the host response to the local inflammatory condition and tissue deterioration in periodontitis, which is a progressive destructive disease of the periodontal tissue potentially leading to multiple tooth loss. In this study, we examined the relationship between aging-induced impairment of MSC function and the severity of periodontal tissue destruction associated with the decrease in host immunomodulatory response using a ligature-induced periodontitis model in young and aged mice. The results of micro computerized tomography (micro-CT) and histological analysis revealed a more severe bone loss associated with increased osteoclast activity in aged (50-week-old) mice compared to young (5-week-old) mice. Immunostaining analysis revealed that, in aged mice, the accumulation of inflammatory T and B cells was higher, whereas the percentage of platelet-derived growth factor receptor α (PDGFRα)⁺ MSCs, which are known to modulate the apoptosis of T cells, was significantly lower than in young mice. In vitro analysis of MSC function showed that the expression of surface antigen markers for MSCs (Sca-1, CD90, CD146), colony formation, migration, and osteogenic differentiation of aged MSCs were significantly declined compared to those of young MSCs. Moreover, a significantly higher proportion of aged MSCs were positive for the senescence-associated β galactosidase activity. Importantly, aged MSCs presented a decreased expression of FAS-L, which was associated with a lower immunomodulatory property of aged MSCs to induce T cell apoptosis in co-cultures compared with young MSCs. In summary, this is the first study showing that aging-induced impairment of MSC function, including immunomodulatory response, is potentially correlated with progressive periodontal tissue deterioration.

Diet-induced Generalized Periodontitis in Lewis Rats

Periodontitis is an important public health concern worldwide. Because rodents from the genus Rattus are resistant to spontaneous periodontitis, experimental periodontitis must be initiated by mechanical procedures and interventions. Due to their exacerbated Th1 response and imbalanced Th17 regulatory T-cell responses, Lewis rats are highly susceptible to inducible inflammatory and autoimmune diseases. We hypothesized that feeding Lewis rats a diet high in sucrose and casein (HSC) would alter the oral microenvironment and induce inflammation and the development of periodontitis lesions without mechanical intervention. A baseline group (BSL, n = 8) was euthanized at age 6 wk. Beginning at 6 wk of age, 2 groups of Lewis rats were fed standard (STD, n = 12) or HSC (n = 20) chow and euthanized at 29 wk of age. We evaluated the degree of periodontitis through histology and μCT of maxillae and mandibles. The HSC-induced inflammatory response of periodontal tissues was assessed by using immunohistochemistry. Gene expression analysis of inflammatory cytokines associated with Th1 and Th17 responses, innate immunity cytokines, and tissue damage in response to bacteria were assessed also. The potential systemic effects of HSC diet were evaluated by assessing body composition and bone densitometry endpoints; serum leptin and insulin concentrations; and gene expression of inflammatory cytokines in the liver. Placing Lewis rats on HSC diet for 24 wk induced a host Th1-immune response in periodontal tissues and mild to moderate, generalized periodontitis characterized by inflammatory cell infiltration (predominantly T cells and macrophages), osteoclast resorption of alveolar bone, and hyperplasia and migration of the gingival epithelium. HSC-fed Lewis rats developed periodontitis without mechanical intervention in the oral cavity and in the absence of any noteworthy metabolic abnormalities. Consequently, the rat model we described here may be a promising approach for modeling mild to moderate periodontitis that is similar in presentation to the human disease.

Microbiome Profiles of Ligature-Induced Periodontitis in Nonhuman Primates across the Life Span

This investigation compared the microbiomes colonizing teeth during the initiation, progression, and resolution of periodontitis in nonhuman primates (Macaca mulatta) at different ages. Subgingival plaque samples were collected at baseline; 0.5, 1, and 3 months following ligature-induced periodontitis; and following naturally occurring disease resolution at 5 months. Samples were analyzed using 16S amplicon sequencing to identify bacterial profiles across age groups: young (<3 years of age), adolescent (3 to 7 years), adult (12 to 15 years), and aged (17 to 23 years). α-Diversity of the microbiomes was greater in the adult/aged samples than in the young/adolescent samples. β-Diversity of the samples demonstrated clear age group differences, albeit individual variation in microbiomes between animals within the age categories was noted. Phylum distributions differed between the young/adolescent animals and the adult/aged animals at each of the time points, showing an enrichment of the phyla Spirochetes, Fusobacteria, and Bacteroidetes associated with periodontitis. Major differences in the top 50 operational taxonomic units (OTUs) were noted in the young and adolescent microbiomes during initiation and progression postligation compared to the adult and aged animals. The proportions of a large number of species in the top 50 OTUs were lower at baseline and in resolved disease microbiomes in the young samples, while profiles in adolescent animals were more consistent with the disease microbiomes. Microbiome profiles for resolution for adults and aged animals appeared more resilient and generally maintained a pattern similar to that of disease. Use of the model can expand our understanding of the crucial interactions of the oral microbiome and host responses in periodontitis.

Sucrose and starch intake contribute to reduced alveolar bone height in a rodent model of naturally occurring periodontitis

While there is a burgeoning interest in the effects of nutrition on systemic inflammatory diseases, how dietary macronutrient balance impacts local chronic inflammatory diseases in the mouth has been largely overlooked. Here, we used the Geometric Framework for Nutrition to test how the amounts of dietary macronutrients and their interactions, as well as carbohydrate type (starch vs sucrose vs resistant starch) influenced periodontitis-associated alveolar bone height in mice. Increasing intake of carbohydrates reduced alveolar bone height, while dietary protein had no effect. Whether carbohydrate came from sugar or starch did not influence the extent of alveolar bone height. In summary, the amount of carbohydrate in the diet modulated periodontitis-associated alveolar bone height independent of the source of carbohydrates.

Complement-Dependent Mechanisms and Interventions in Periodontal Disease

Periodontitis is a prevalent inflammatory disease that leads to the destruction of the tooth-supporting tissues. Current therapies are not effective for all patients and this oral disease continues to be a significant public health and economic burden. Central to periodontal disease pathogenesis is a reciprocally reinforced interplay between microbial dysbiosis and destructive inflammation, suggesting the potential relevance of host-modulation therapies. This review summarizes and discusses clinical observations and pre-clinical intervention studies that collectively suggest that complement is hyperactivated in periodontitis and that its inhibition provides a therapeutic benefit. Specifically, interception of the complement cascade at its central component, C3, using a locally administered small peptidic compound (Cp40/AMY-101) protected non-human primates from induced or naturally occurring periodontitis. These studies indicate that C3-targeted intervention merits investigation as an adjunctive treatment of periodontal disease in humans.

Mutual interplay between IL-17-producing γδT cells and microbiota orchestrates oral mucosal homeostasis

γδT cells are a major component of epithelial tissues and play a role in tissue homeostasis and host defense. γδT cells also reside in the gingiva, an oral tissue covered with specialized epithelium that continuously monitors the challenging dental biofilm. Whereas most research on intraepithelial γδT cells focuses on the skin and intestine epithelia, our knowledge on these cells in the gingiva is still incomplete. In this study, we demonstrate that even though the gingiva develops after birth, the majority of gingival γδT cells are fetal thymus-derived Vγ6+ cells, and to a lesser extent Vγ1+ and Vγ4+ cells. Furthermore, we show that γδT cells are motile and locate preferentially in the epithelium adjacent to the biofilm. Vγ6+ cells represent the major source of IL-17-producing cells in the gingiva. Chimeric mice and parabiosis experiments indicated that the main fraction of gingival γδT cells is radioresistant and tissue-resident, persisting locally independent of circulating γδT cells. Notably, gingival γδT cell homeostasis is regulated by the microbiota as the ratio of Vγ6+ and Vγ4+ cells was reversed in germ-free mice, and their activation state was decreased. As a consequence, conditional ablation of γδT cells results in elevated gingival inflammation and subsequent alterations of oral microbial diversity. Taken together, these findings suggest that oral mucosal homeostasis is shaped by reciprocal interplays between γδT cells and local microbiota.

Age and Periodontal Health - Immunological View

PURPOSE OF THE REVIEW

Aging clearly impacts a wide array of systems, in particular the breadth of the immune system leading to immunosenescence, altered immunoactivation, and coincident inflammaging processes. The net result of these changes leads to increased susceptibility to infections, increased neoplastic occurrences, and elevated frequency of autoimmune diseases with aging. However, as the bacteria in the oral microbiome that contribute to the chronic infection of periodontitis is acquired earlier in life, the characteristics of the innate and adaptive immune systems to regulate these members of the autochthonous microbiota across the lifespan remains ill defined.

RECENT FINDINGS

Clear data demonstrate that both cells and molecules of the innate and adaptive immune response are adversely impacted by aging, including in the oral cavity, yielding a reasonable tenet that the increased periodontitis noted in aging populations is reflective of the age-associated immune dysregulation. Additionally, this facet of host-microbe interactions and disease needs to accommodate the population variation in disease onset and progression, which may also reflect an accumulation of environmental stressors and/or decreased protective nutrients that could function at the gene level (ie. epigenetic) or translational level for production and secretion of immune system molecules.

SUMMARY

Finally, the majority of studies of aging and periodontitis have emphasized the increased prevalence/severity of disease with aging, all based upon chronological age. However, evolving areas of study focusing on "biological aging" to help account for population variation in disease expression, may suggest that chronic periodontitis represents a co-morbidity that contributes to "gerovulnerability" within the population.

Comparative analysis of expression of microbial sensing molecules in mucosal tissues with periodontal disease

Host-derived pattern recognition receptors (PRRs) are necessary for effective innate immune engagement of pathogens that express microbial-associated molecular patterns (MAMP) ligands for these PRRs. This study used a nonhuman primate model to evaluate the expression of these sensing molecules in gingival tissues. Macaca mulatta aged 12-24 with a healthy periodontium (n = 13) or periodontitis (n = 11) provided gingival tissues for assessment of naturally-occurring periodontitis. An additional group of animals (12-23 years; n = 18) was subjected to a 5 month longitudinal study examining the initiation and progression of periodontitis, RNA was isolated and microarray analysis conducted for gene expression of the sensing PRRs. The results demonstrated increased expression of various PRRs in naturally-occurring established periodontitis. Selected PRRs also correlated with both bleeding on probing (BOP) and pocket depth (PD) in the animals. The longitudinal model demonstrated multiple TLRs, as well as selected other PRRs that were significantly increased by 2 weeks during initiation of the lesion. While gene expression levels of various PRRs correlated with BOP and PD at baseline and resolution of disease, few correlated with these clinical parameters during initiation and progression of the lesion. These findings suggest that the levels of various PRRs are affected in established periodontitis lesions, and that PRR expression increased most dramatically during the initiation of the disease process, presumably in response to the juxtaposed microbial challenge to the tissues and goal of reestablishing homeostasis.

Amphiregulin-producing γδ T cells are vital for safeguarding oral barrier immune homeostasis

Loss of oral barrier homeostasis leads to the development of periodontitis, the most common chronic inflammatory condition of mankind. Therefore, it is important to better understand the immune mediators acting at this unique barrier to safeguard tissue integrity. Here we identify a vital role for γδ T cells in constraining pathological inflammation at the oral barrier, as the absence of γδ T cells resulted in enhanced pathology during periodontitis. We show that oral barrier γδ T cells produce the reparative cytokine Amphiregulin, administration of which rescued the elevated oral pathology of tcrδ^−/− mice. Collectively, we identify a pathway controlling oral immunity mediated by barrier-resident γδ T cells, highlighting that these cells are crucial guards of oral barrier immune homeostasis.

γδ T cells are enriched at barrier sites such as the gut, skin, and lung, where their roles in maintaining barrier integrity are well established. However, how these cells contribute to homeostasis at the gingiva, a key oral barrier and site of the common chronic inflammatory disease periodontitis, has not been explored. Here we demonstrate that the gingiva is policed by γδ T cells with a T cell receptor (TCR) repertoire that diversifies during development. Gingival γδ T cells accumulated rapidly after birth in response to barrier damage, and strikingly, their absence resulted in enhanced pathology in murine models of the oral inflammatory disease periodontitis. Alterations in bacterial communities could not account for the increased disease severity seen in γδ T cell-deficient mice. Instead, gingival γδ T cells produced the wound healing associated cytokine amphiregulin, administration of which rescued the elevated oral pathology of tcrδ^−/− mice. Collectively, our results identify γδ T cells as critical constituents of the immuno-surveillance network that safeguard gingival tissue homeostasis.

Differential Mechanism of Periodontitis Progression in Postmenopause

Over the past four decades, it has become accepted that periodontal disease is caused by specific bacterial infections and that individuals are uniformly susceptible neither to these infections nor to the damage caused by them. The specific bacterial infections and the composition of the environment in which these bacteria easily settle cause an immune response. The immune cells involved in pathogenesis of periodontitis migrate into the periodontitis lesion and advance the disease. The purpose of the present study is to investigate the correlation between immune cell migration and progression of periodontal disease by inducing estrogen deficiency through ovariectomy (OVX) to mimic postmenopausal women and treatment with lipopolysaccharide (LPS). The LPS derived from Porphyromonas gingivalis induced periodontitis and absorption of the alveolar bone dose-dependently. However, the alveolar crest level reduction after LPS injection between OVX and Sham operated mice did not show a significant difference. Matrix metallopeptidase-9 (MMP-9), which is known to be able to detect the progression of periodontitis in general, was not significantly different between OVX and Sham groups. However, immune cells such as T-lymphocytes and neutrophils migrated less overall in OVX groups than Sham operated groups. These findings can be a topic of debate on the old controversy regarding the relationship between periodontal disease and hormonal change. Currently, in clinical practice, menopause is not a major consideration in the treatment of periodontal disease. This study suggests that treatment methods and medication should be considered in the treatment of infectious periodontal disease in postmenopausal women.

Ageing effects on humoral immune responses in chronic periodontitis

Periodontal disease is a dominant global bacterial infection that increases with ageing.

AIM

This report focuses on host adaptive immune responses in periodontitis. While experimental models and humans diagnosed with periodontitis demonstrate an antigenic specificity for particular oral bacteria, we have a limited understanding of (i) how ageing affects the adaptive immune responses to these bacteria that chronically colonize the oral cavity for decades prior to disease expression and (ii) how the magnitude and specificity of the response interface with pathogens that emerge within the bacterial ecology during exacerbations of disease.

MATERIALS AND METHODS

Serum antibody levels to a group of pathogenic and commensal oral bacteria were measured in a population of individuals from 21 to 74 years of age, stratified based on clinical status of the periodontium, smoking and sex.

RESULTS

Clinical parameters were not significantly different within health, gingivitis or periodontitis groups related to age. Antibody to oral pathogens and commensals was similar in different age groups in each of the clinical categories, with no age correlation noted in the periodontitis patients.

CONCLUSIONS

The adaptive immune responses to oral bacteria that chronically colonize the oral cavity appear generally unaffected by age, but clearly are linked to the extent of disease.

Oral health in geroscience: animal models and the aging oral cavity

Age is the single greatest risk factor for many diseases, including oral diseases. Despite this, a majority of preclinical oral health research has not adequately considered the importance of aging in research aimed at the mechanistic understanding of oral disease. Here, we have attempted to provide insights from animal studies in the geroscience field and apply them in the context of oral health research. In particular, we discuss the relationship between the biology of aging and mechanisms of oral disease. We also present a framework for defining and utilizing age-appropriate rodents and present experimental design considerations, such as the number of age-points used and the importance of genetic background. While focused primarily on rodent models, alternative animal models that may be particularly useful for studies of oral health during aging, such as companion dogs and marmoset monkeys, are also discussed. We hope that such information will aid in the design of future preclinical studies of geriatric dental health, thus allowing more reliability for translation of such studies to age-associated oral disease in people.

Sequential BMP7/TGF-β1 signaling and microbiota instruct mucosal Langerhans cell differentiation

Capucha et al. demonstrate that mucosal Langerhans cell (LC) differentiation from pre–dendritic cells and monocytes involves consecutive BMP7 and TGF-β1 signaling in separate anatomical locations. Moreover, mucosal microbiota regulates the development of LCs that in turn shape microbial and immunological homeostasis.

Mucosal Langerhans cells (LCs) originate from pre–dendritic cells and monocytes. However, the mechanisms involved in their in situ development remain unclear. Here, we demonstrate that the differentiation of murine mucosal LCs is a two-step process. In the lamina propria, signaling via BMP7-ALK3 promotes translocation of LC precursors to the epithelium. Within the epithelium, TGF-β1 finalizes LC differentiation, and ALK5 is crucial to this process. Moreover, the local microbiota has a major impact on the development of mucosal LCs, whereas LCs in turn maintain mucosal homeostasis and prevent tissue destruction. These results reveal the differential and sequential role of TGF-β1 and BMP7 in LC differentiation and highlight the intimate interplay of LCs with the microbiota.

Rapamycin treatment attenuates age-associated periodontitis in mice

Interventions that target biological mechanisms of aging have great potential to enhance quality of life by delaying morbidity and mortality. The FDA-approved drug rapamycin is a compelling candidate for such an intervention. In a previous study, it was reported that 3 months of rapamycin treatment is sufficient to increase life expectancy and remodel the gut microbiome in aged mice. Transient treatment with rapamycin or a rapamycin derivative has also been shown to delay immune stem cell senescence and rejuvenate immune function in aged mice and elderly people. Periodontal disease is an important age-related disease involving altered immune function, pathological changes to the oral microbiome, and systemic inflammation. Periodontal disease is defined clinically by loss of alveolar bone and by connective tissue degeneration. Here, we describe significant alveolar bone loss during aging in two different mouse strain backgrounds and report that rapamycin treatment is sufficient to reverse age-associated periodontal disease in mice. Partial restoration of youthful levels of alveolar bone is observed in 22-month-old rapamycin-treated mice as rapidly as 8 weeks after initiation of treatment. To the best of our knowledge, this represents the first intervention shown to substantially prevent or reverse age-associated alveolar bone loss. These findings suggest the possibility that inhibition of mTOR with rapamycin or other pharmacological agents may be useful to treat a clinically relevant condition for which there is currently no effective treatment.

From restoration to regeneration: periodontal aging and opportunities for therapeutic intervention

With the march of time our bodies start to wear out: eyesight fades, skin loses its elasticity, teeth and bones become more brittle and injuries heal more slowly. These universal features of aging can be traced back to our stem cells. Aging has a profound effect on stem cells: DNA mutations naturally accumulate over time and our bodies have evolved highly specialized mechanisms to remove these damaged cells. Whilst obviously beneficial, this repair mechanism also reduces the pool of available stem cells and this, in turn, has a dramatic effect on tissue homeostasis and on our rate of healing. Simply put: fewer stem cells means a decline in tissue function and slower healing. Despite this seemingly intractable situation, research over the past decade now demonstrates that some of the effects of aging are reversible. Nobel prize-winning research demonstrates that old cells can become young again, and lessons learned from these experiments-in-a-dish are now being translated into human therapies. Scientists and clinicians around the world are identifying and characterizing methods to activate stem cells to reinvigorate the body's natural regenerative process. If this research in dental regenerative medicine pans out, the end result will be tissue homeostasis and healing back to the levels we appreciated when we were young.

Transcriptome Analysis of B Cell Immune Functions in Periodontitis: Mucosal Tissue Responses to the Oral Microbiome in Aging

Evidence has shown activation of T and B cells in gingival tissues in experimental models and in humans diagnosed with periodontitis. The results of this adaptive immune response are noted both locally and systemically with antigenic specificity for an array of oral bacteria, including periodontopathic species, e.g., Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans. It has been recognized through epidemiological studies and clinical observations that the prevalence of periodontitis increases with age. This report describes our studies evaluating gingival tissue transcriptomes in humans and specifically exploiting the use of a non-human primate model of naturally occurring periodontitis to delineate gingival mucosal tissue gene expression profiles focusing on cells/genes critical for the development of humoral adaptive immune responses. Patterns of B cell and plasmacyte genes were altered in aging healthy gingival tissues. Substantial increases in a large number of genes reflecting antigen-dependent activation, B cell activation, B cell proliferation, and B cell differentiation/maturation were observed in periodontitis in adults and aged animals. Finally, evaluation of the relationship of these gene expression patterns with those of various tissue destructive molecules (MMP2, MMP9, CTSK, TNFα, and RANKL) showed a greater frequency of positive correlations in healthy tissues versus periodontitis tissues, with only MMP9 correlations similar between the two tissue types. These results are consistent with B cell response activities in healthy tissues potentially contributing to muting the effects of the tissue destructive biomolecules, whereas with periodontitis this relationship is adversely affected and enabling a progression of tissue destructive events.

Ethical guidelines, animal profile, various animal models used in periodontal research with alternatives and future perspectives

Laboratory animal models serve as a facilitator to investigate the etiopathogenesis of periodontal disease, are used to know the efficacy of reconstructive and regenerative procedures, and are also helpful in evaluation of newer therapeutic techniques including laser and implant therapies prior to application in the human beings. The aim of this review is to know the different animal models used in various specialties of dental research and to know the ethical guidelines prior to the usage of experimental models with main emphasis on how to refine, replace, and reduce the number of animal models usage in the laboratory. An online search for experimental animal models used in dental research was performed using MEDLINE/PubMed database. Publications from 2009 to May 2013 in the specialty of periodontics were included in writing this review. A total of 652 references were published in PubMed/MEDLINE databases based on the search terms used. Out of 245 studies, 241 were related to the periodontal research published in English from 2009 to 2013. Relevant papers were chosen according to the inclusion and exclusion criteria. After extensive electronic and hand search on animal models, it has been observed that various animal models were used in dental research. Search on animal models used for dental research purpose revealed that various animals such as rats, mice, guinea pigs, rabbit, beagle dogs, goats, and nonhuman primates were extensively used. However, with the new advancement of ex vivo animal models, it has become easy to investigate disease pathogenesis and to test the efficacy of newer therapeutic modalities with the reduced usage of animal models. This review summarized the large amount of literature on animal models used in periodontal research with main emphasis on ethical guidelines and on reducing the animal model usage in future perspective.

Variants of Porphyromonas gingivalis lipopolysaccharide alter lipidation of autophagic protein, microtubule-associated protein 1 light chain 3, LC3

Porphyromonas gingivalis often subverts host cell autophagic processes for its own survival. Our previous studies document the association of the cargo sorting protein, melanoregulin (MREG), with its binding partner, the autophagic protein, microtubule-associated protein 1 light chain 3 (LC3) in macrophages incubated with P. gingivalis (strain 33277). Differences in the lipid A moiety of lipopolysaccharide (LPS) affect the virulence of P. gingivalis; penta-acylated LPS₁₆₉₀ is a weak Toll-like receptor 4 agonist compared with Escherichia coli LPS, whereas tetra-acylated LPS_1435/1449 acts as an LPS₁₆₉₀ antagonist. To determine how P. gingivalis LPS₁₆₉₀ affects autophagy we assessed LC3-dependent and MREG-dependent processes in green fluorescent protein (GFP)-LC3-expressing Saos-2 cells. LPS₁₆₉₀ stimulated the formation of very large LC3-positive vacuoles and MREG puncta. This LPS₁₆₉₀ -mediated LC3 lipidation decreased in the presence of LPS_1435/1449 . When Saos-2 cells were incubated with P. gingivalis the bacteria internalized but did not traffic to GFP-LC3-positive structures. Nevertheless, increases in LC3 lipidation and MREG puncta were observed. Collectively, these results suggest that P. gingivalis internalization is not necessary for LC3 lipidation. Primary human gingival epithelial cells isolated from patients with periodontitis showed both LC3II and MREG puncta whereas cells from disease-free individuals exhibited little co-localization of these two proteins. These results suggest that the prevalence of a particular LPS moiety may modulate the degradative capacity of host cells, so influencing bacterial survival.

Association between periodontal disease and inflammatory arthritis reveals modulatory functions by melanocortin receptor type 3

Because there is clinical evidence for an association between periodontal disease and rheumatoid arthritis, it is important to develop suitable experimental models to explore pathogenic mechanisms and therapeutic opportunities. The K/BxN serum model of inflammatory arthritis was applied using distinct protocols, and modulation of joint disruption afforded by dexamethasone and calcitonin was established in comparison to the melanocortin (MC) receptor agonist DTrp(8)-γ-melanocyte stimulating hormone (MSH; DTrp). Wild-type and MC receptor type 3 (MC3)-null mice of different ages were also used. There was significant association between severity of joint disease, induced with distinct protocols and volumes of the arthritogenic K/BxN serum, and periodontal bone damage. Therapeutic treatment with 10 μg dexamethasone, 30 ng elcatonin, and 20 μg DTrp per mouse revealed unique and distinctive pharmacological properties, with only DTrp protecting both joint and periodontal tissue. Further analyses in nonarthritic animals revealed higher susceptibility to periodontal bone loss in Mc3r(-/-) compared with wild-type mice, with significant exacerbation at 14 weeks of age. These data reveal novel protective properties of endogenous MC3 on periodontal status in health and disease and indicate that MC3 activation could lead to the development of a new genus of anti-arthritic bone-sparing therapeutics.

Aging and its Impact on Innate Immunity and Inflammation: Implications for Periodontitis

The elderly exhibit increased susceptibility to a number of inflammatory or degenerative pathologies. Aging is similarly thought to be associated with increased prevalence and severity of periodontitis, although the underlying causes are poorly understood. Among the plausible mechanisms whereby aging could contribute to increased susceptibility to periodontitis are age-dependent alterations in the innate immune and inflammatory status of the host. This hypothesis is supported by studies in humans and animal models outlined in this Review. Indeed, innate immune cells isolated from elderly subjects exhibit age-related cell-intrinsic defects that could predispose the elderly to deregulated immune and inflammatory responses. Moreover, the investigation of age-related alterations in the tissue environment where recruited inflammatory cells ultimately function could provide complementary, if not better, insights into the impact of aging on periodontitis. Integrative approaches combining in vitro and in vivo mechanistic models are underway and can potentially contribute to targeted molecular therapies that can reverse or mitigate the effects of aging on periodontitis and other inflammatory diseases.

Dendritic cells of the oral mucosa

The oral cavity contains distinct mucosal surfaces, each with its own unique distribution of dendritic cell (DC) subsets. In addition to tissue-specific properties, such organization might confer differential immune outcomes guided by tissue-resident DCs, which translate in the lymph node into an overall immune response. This process is further complicated by continual exposure and colonization of the oral cavity with enormous numbers of diverse microbes, some of which might induce destructive immunity. As a central cell type constantly monitoring changes in oral microbiota and orchestrating T-cell function, oral DCs are of major importance in deciding whether to induce immunity or tolerance. In this review, an overview of the phenotype and distribution of DCs in the oral mucosa is provided. In addition, the role of the various oral DC subsets in inducing immunity vs. tolerance, as well as their involvement in several oral pathologies is discussed.

Loss of dentin sialophosphoprotein leads to periodontal diseases in mice

BACKGROUND AND OBJECTIVE

Dentin sialophosphoprotein (DSPP) and its cleaved products, dentin phosphoprotein (DPP) and dentin sialoprotein (DSP), play important roles in biomineralization. Recently, we observed that DSPP is highly expressed in the alveolar bone and cementum, indicating that this molecule may play an important role in the formation and maintenance of a healthy periodontium, and its deletion may cause increased susceptibility to periodontal diseases. The objective of this investigation was to study the effects of Dspp ablation on periodontal tissues by analyzing Dspp null mice.

MATERIAL AND METHODS

Newborn to 6-mo-old Dspp null mice were examined, and the 3- and 6-mo-old Dspp null mice were characterized in detail using X-ray radiography, histology and scanning electron microscopy (backscattered as well as resin-infiltrating). Wild-type mice of the same age groups served as the normal controls.

RESULTS

The Dspp null mice showed significant loss of alveolar bone and cementum, particularly in the furcation and interproximal regions of the molars. The alveolar bone appeared porous while the quantity of cementum was reduced in the apical region. The canalicular systems and osteocytes in the alveolar bone were abnormal, with reduced numbers of canaliculi and altered osteocyte morphology. The loss of alveolar bone and cementum along with the detachment of the periodontal ligaments (PDL) led to the apical migration of the epithelial attachment and formation of periodontal pockets.

CONCLUSION

Inactivation of DSPP leads to the loss of alveolar bone and cementum and increased susceptibility to bacterial infections in PDL of Dspp null mice. The fact that the loss of DSPP results in periodontal diseases indicates that this molecule plays a vital role in maintaining the health of the periodontium.

Association between polymorphisms in interleukin-17A and -17F genes and chronic periodontal disease

OBJECTIVE

Interleukin-17 (IL-17) is a cytokine that induces neutrophil recruitment and the release of inflammatory mediators in several inflammatory conditions; nevertheless, the involvement of IL-17 gene polymorphisms in chronic periodontitis (CP) has not been addressed yet. Our aim was to evaluate the association between periodontal status and the polymorphisms IL-17A G197A and IL-17F C7488T in subjects with CP along with their impact on levels of inflammatory mediators.

MATERIAL AND METHODS

Genomic DNA was obtained from 30 CP patients and 30 healthy controls (HCs). IL-17A G197A and IL-17F C7488T polymorphisms were determined using PCR-RFLP. Serum and periodontal tissues were collected and processed for ELISA, myeloperoxidase (MPO), and/or microscopic analysis.

RESULTS

The frequencies of genotypes in the CP group were significantly different from those of HC. Odds ratio indicated that increased risks for CP were associated with the -197A allele, not with the -7488T allele. In addition, the -197A allele was correlated with worse clinical parameters, higher MPO activity, and increased expression of inflammatory mediators (IL-17A and IL-8) than the other genotypes.

CONCLUSIONS

These results indicate that the IL-17A -197A allele is associated with increased risk for CP, likely because this genotype relates to the enhanced inflammation in periodontal tissues.

Age-related increase in food spilling by laboratory mice may lead to significant overestimation of actual food consumption: implications for studies on dietary restriction, metabolism, and dose calculations

It is widely accepted that food consumption in humans declines with advanced age; however, data from mice remain controversial. Based on our previous observation that mice spill a considerable amount of food while eating, we hypothesized that increased food spillage in old mice masks actual food intake. To investigate whether mice exhibit age-associated declines in food consumption, we evaluated the actual food consumption of C57BL/6 mice at various ages by measuring both the amount of food in the food receptacle and the amount dropped to the cage bottom during feeding. We found that old mice dropped significantly more food (36% ± 8%) than young mice (18% ± 5%), which led to overestimations of food consumption, particularly in old mice. Although actual food consumption decreased in very old mice, food intake per body weight did not significantly change. These findings suggest that caution should be taken to accurately quantify food consumption by aged animals.

The leukocyte integrin antagonist Del-1 inhibits IL-17-mediated inflammatory bone loss

Aging is linked to greater susceptibility to chronic inflammatory diseases, several of which, including periodontitis, involve neutrophil-mediated tissue injury. Here we found that aging-associated periodontitis was accompanied by lower expression of Del-1, an endogenous inhibitor of neutrophil adhesion dependent on the integrin LFA-1, and by reciprocal higher expression of interleukin 17 (IL-17). Consistent with that, IL-17 inhibited gingival endothelial cell expression of Del-1, thereby promoting LFA-1-dependent recruitment of neutrophils. Young Del-1-deficient mice developed spontaneous periodontitis that featured excessive neutrophil infiltration and IL-17 expression; disease was prevented in mice doubly deficient in Del-1 and LFA-1 or in Del-1 and the IL-17 receptor. Locally administered Del-1 inhibited IL-17 production, neutrophil accumulation and bone loss. Therefore, Del-1 suppressed LFA-1-dependent recruitment of neutrophils and IL-17-triggered inflammatory pathology and may thus be a promising therapeutic agent for inflammatory diseases.

Enhanced alveolar bone loss in a model of non-invasive periodontitis in rice rats

OBJECTIVE

The rice rat (Oryzomys palustris) develops periodontitis-like lesions when fed a diet rich in sucrose and casein (H-SC). We aimed to establish whether this model can accurately mimic the development of human periodontitis.

MATERIALS AND METHODS

For this purpose, 28-day-old rice rats (15/group) were assigned to standard (STD) or H-SC diets and sacrificed after 6, 12, and 18 weeks. Jaws were processed for morphometric, histometric, histologic, histomorphometric, and micro-CT analyses.

RESULTS

We found a progressive increase in horizontal alveolar bone loss (ABL) with age in maxillae of rats fed the STD diet as determined by morphometry. The H-SC diet exacerbated horizontal ABL at the palatal surface at 12 and 18 weeks. Furthermore, increased vertical ABL was detected in mandibles and maxillae of rats fed the H-SC diet for 12 and/or 18 weeks by histometry and micro-CT. Remarkably, the H-SC diet significantly increased bone remodeling at the interproximal alveolar bone of mandibles from rats fed for 6 weeks, but not in those fed for longer periods.

CONCLUSIONS

These findings indicate that the H-SC diet induced a transient increase in alveolar bone remodeling, which is followed by ABL characteristic of moderate periodontitis.

Altered Toll-like receptor 2-mediated endotoxin tolerance is related to diminished interferon beta production

Induction of endotoxin tolerance leads to a reduced inflammatory response after repeated challenge by LPS and is important for resolution of inflammation and prevention of tissue damage. Enterobacterial LPS is recognized by the TLR4 signaling complex, whereas LPS of some non-enterobacterial organisms is capable of signaling independently of TLR4 utilizing TLR2-mediated signal transduction instead. In this study we report that Porphyromonas gingivalis LPS, a TLR2 agonist, fails to induce a fully endotoxin tolerant state in a human monocytic cell line (THP-1) and mouse bone marrow-derived macrophages. In contrast to significantly decreased production of human IL-8 and TNF-α and, in mice, keratinocyte-derived cytokine (KC), macrophage inflammatory protein-2 (MIP-2), and TNF-α after repeated challenge with Escherichia coli LPS, cells repeatedly exposed to P. gingivalis LPS responded by producing less TNF-α but sustained elevated secretion of IL-8, KC, and MIP-2. Furthermore, in endotoxin-tolerant cells, production of IL-8 is controlled at the signaling level and correlates well with NF-κB activation, whereas TNF-α expression is blocked at the gene transcription level. Interferon β plays an important role in attenuation of chemokine expression in endotoxin-tolerized cells as shown in interferon regulatory factor-3 knock-out mice. In addition, human gingival fibroblasts, commonly known not to display LPS tolerance, were found to be tolerant to repeated challenge by LPS if pretreated with interferon β. The data suggest that the inability of the LPS-TLR2 complex to induce full endotoxin tolerance in monocytes/macrophages is related to diminished production of interferon β and may partly explain the involvement of these LPS isoforms in the pathogenesis of chronic inflammatory diseases.

The C5a receptor impairs IL-12-dependent clearance of Porphyromonas gingivalis and is required for induction of periodontal bone loss

The C5a anaphylatoxin receptor (C5aR; CD88) is activated as part of the complement cascade and exerts important inflammatory, antimicrobial, and regulatory functions, at least in part, via crosstalk with TLRs. However, the periodontal pathogen Porphyromonas gingivalis can control C5aR activation by generating C5a through its own C5 convertase-like enzymatic activity. In this paper, we show that P. gingivalis uses this mechanism to proactively and selectively inhibit TLR2-induced IL-12p70, whereas the same pathogen-instigated C5aR-TLR2 crosstalk upregulates other inflammatory and bone-resorptive cytokines (IL-1β, IL-6, and TNF-α). In vivo, the ability of P. gingivalis to manipulate TLR2 activation via the C5a-C5aR axis allowed it to escape IL-12p70-dependent immune clearance and to cause inflammatory bone loss in a murine model of experimental periodontitis. In the latter regard, C5aR-deficient or TLR2-deficient mice were both resistant to periodontal bone loss, in stark contrast with wild-type control mice, which is consistent with the interdependent interactions of C5aR and TLR2 in P. gingivalis immune evasion and induction of bone-resorptive cytokines. In conclusion, P. gingivalis targets C5aR to promote its adaptive fitness and cause periodontal disease. Given the current availability of safe and effective C5aR antagonists, pharmacological blockade of C5aR could act therapeutically in human periodontitis and reduce associated systemic risks.

Aging and bone

Bones provide mechanical and protective function, while also serving as housing for marrow and a site for regulation of calcium ion homeostasis. The properties of bones do not remain constant with age; rather, they change throughout life, in some cases improving in function, but in others, function deteriorates. Here we review the modifications in the mechanical function and shape of bones, the bone cells, the matrix they produce, and the mineral that is deposited on this matrix, while presenting recent theories about the factors leading to these changes.

Destructive and protective roles of cytokines in periodontitis: a re-appraisal from host defense and tissue destruction viewpoints

Periodontal diseases (PD) are chronic infectious inflammatory diseases characterized by the destruction of tooth-supporting structures, being the presence of periodontopathogens required, but not sufficient, for disease development. As a general rule, host inflammatory mediators have been associated with tissue destruction, while anti-inflammatory mediators counteract and attenuate disease progression. With the discovery of several T-cell subsets bearing distinct immunoregulatory properties, this pro- vs. anti-inflammatory scenario became more complex, and a series of studies has hypothesized protective or destructive roles for Th1, Th2, Th17, and Treg subpopulations of polarized lymphocytes. Interestingly, the "protective vs. destructive" archetype is usually considered in a framework related to tissue destruction and disease progression. However, it is important to remember that periodontal diseases are infectious inflammatory conditions, and recent studies have demonstrated that cytokines (TNF-α and IFN-γ) considered harmful in the context of tissue destruction play important roles in the control of periodontal infection. Therefore, in this review, the state-of-the-art knowledge concerning the protective and destructive roles of host inflammatory immune response will be critically evaluated and discussed from the tissue destruction and control-of-infection viewpoints.

Too old to fight? Aging and its toll on innate immunity

Elderly individuals display increased susceptibility to chronic inflammatory diseases and microbial infections, such as periodontitis and oral aspiration pneumonia. The resurgent interest in innate immunity in the 2000s has been accompanied by parallel studies to understand the impact of aging on the function of the innate immune system, which not only provides first-line defense but is essential for the development of adaptive immunity. This review summarizes and discusses our current understanding of age-associated molecular alterations in neutrophils and macrophages, key inflammatory phagocytes implicated in both protective and destructive host responses. The analysis of recent literature suggests that, in advanced age, phagocytes undergo significant changes in signal transduction pathways that may affect their ability to perform antimicrobial functions or regulate the inflammatory response. These abnormalities are expected to contribute to the pathology of oral infection-driven inflammatory diseases in the elderly. Moreover, the elucidation of age-associated defects in the innate immune system will facilitate the development of intervention therapeutic strategies to promote or restore innate immune function and improve the quality of health in old age.

Complement and periodontitis

Although the complement system is centrally involved in host defense, its overactivation or deregulation (e.g., due to inherent host genetic defects or due to pathogen subversion) may excessively amplify inflammation and contribute to immunopathology. Periodontitis is an oral infection-driven chronic inflammatory disease which exerts a systemic impact on health. This paper reviews evidence linking complement to periodontal inflammation and pathogenesis. Clinical and histological observations show a correlation between periodontal inflammatory activity and local complement activation. Certain genetic polymorphisms or deficiencies in specific complement components appear to predispose to increased susceptibility to periodontitis. Animal model studies and in vitro experiments indicate that periodontal bacteria can either inhibit or activate distinct components of the complement cascade. Porphyromonas gingivalis, a keystone species in periodontitis, subverts complement receptor 3 and C5a anaphylatoxin receptor signaling in ways that promote its adaptive fitness in the presence of non-productive inflammation. Overall, available evidence suggests that complement activation or subversion contributes to periodontal pathogenesis, although not all complement pathways or functions are necessarily destructive. Effective complement-targeted therapeutic intervention in periodontitis would require determining the precise roles of the various inductive or effector complement pathways. This information is essential as it may reveal which specific pathways need to be blocked to counteract microbial evasion and inflammatory pathology or, conversely, kept intact to promote host immunity.

Too old to fight? Aging and its toll on innate immunity

Elderly individuals display increased susceptibility to chronic inflammatory diseases and microbial infections, such as periodontitis and oral aspiration pneumonia. The resurgent interest in innate immunity in the 2000s has been accompanied by parallel studies to understand the impact of aging on the function of the innate immune system, which not only provides first-line defense but is essential for the development of adaptive immunity. This review summarizes and discusses our current understanding of age-associated molecular alterations in neutrophils and macrophages, key inflammatory phagocytes implicated in both protective and destructive host responses. The analysis of recent literature suggests that, in advanced age, phagocytes undergo significant changes in signal transduction pathways that may affect their ability to perform antimicrobial functions or regulate the inflammatory response. These abnormalities are expected to contribute to the pathology of oral infection-driven inflammatory diseases in the elderly. Moreover, the elucidation of age-associated defects in the innate immune system will facilitate the development of intervention therapeutic strategies to promote or restore innate immune function and improve the quality of health in old age.